loginservlet连接数据库时的异常

public class LoginServlet extends HttpServlet {    /**     *      */    private static final long serialVersionUID = 1L;    private DataBase database = null;    //初始化函数    public void init() throws ServletException {        database = new DataBase();    }    //处理get请求方法    public void doGet(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        doPost(request, response);    }    //处理post请求方法    public void doPost(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        HttpSession session = request.getSession();       //获取用户当前会话        String username = "";                                    String password = "";        String page = null;        if(request.getParameter("txtUserName") != null)            username = request.getParameter("txtUserName");  //获取用户名        if(request.getParameter("txtPassword") != null)            password = request.getParameter("txtPassword");  //获取密码        //判断用户名、密码是否匹配        boolean temp = false;        //System.out.println(username + ", " + password);        Connection con = database.getConnection();        temp = DBUtilitya.isValid(con, username, password);        //关闭数据库连接        database.closeConnection(con);        if(temp){            InfoItem infoitem = null;            Connection con2 = database.getConnection();            infoitem = DBUtilitya.getUser(con2, username);            database.closeConnection(con2);            //将用户信息对象InfoItem存储在session对象当中            session.setAttribute("infoitem",infoitem);            //如果用户通过验证，则返回用户有关信息            page = "showinfo.jsp";        } else{            //如果验证失败，则显示验证失败页面            page = "errorpage.jsp";        }        //重定向到相应的页面        response.sendRedirect(page);        return;    }}

public class DBUtilitya {    //判断用户名、密码是否正确    public static boolean isValid(Connection con, String username, String userpwd){        PreparedStatement prepStmt = null;        ResultSet rs = null;                //存储查询结果        String selectStatement = "select * from userinfo1 where  username='" +username+"' and userpwd = '" +userpwd+"' ";        boolean temp = false;        try{           prepStmt = con.prepareStatement(selectStatement);           prepStmt.setString(1,username);           prepStmt.setString(2,userpwd);           rs = prepStmt.executeQuery();     //查询数据库并返回结果记录集           if (rs.next())                    //数据库里含有此用户名、密码对则返回true              temp = true;           else              temp = false;                  //否则返回false,用户名、密码不匹配           rs.close();           prepStmt.close();        }catch(Exception e){           e.printStackTrace();        }        return temp;                         //返回验证结果    }    //根据用户名从数据库中获取用户的注册信息    public static InfoItem getUser(Connection con, String username){        PreparedStatement prepStmt = null;        ResultSet rs = null;                 //结果记录集合        InfoItem infoitem = null;        String queryString = "select username,roomnumber1,roomnumber2, roomnumber3, roomnumber4 from userinfo1 where username='" +username+"'";        try{           prepStmt = con.prepareStatement(queryString);           prepStmt.setString(1, username);           rs = prepStmt.executeQuery();     //查询数据库并返回结果记录集合           if(rs.next())           {                   //数据库里含有此用户名、密码对则返回InfoItem对象               infoitem = new InfoItem(rs.getString("username"),                                       rs.getString("roomnumber1"),                                       rs.getString("roomnumber2"),                                       rs.getString("roomnumber3"),                                       rs.getString("roomnumber4")                                       );           } else {                         //否则返回null               infoitem = null;           }           rs.close();           prepStmt.close();        }catch(Exception e){           e.printStackTrace();        }        return infoitem;           }